The invention concerns a method for operating an X-ray or neutron-optical system with an X-ray or neutron source from which associated radiation is guided as a primary beam to a sample under investigation, and with an X-ray or neutron detector for receiving radiation diffracted or scattered from the sample, wherein the source, the sample and the detector are substantially disposed on one line (=z-axis), and wherein a beam stop is provided between the sample and the detector, whose cross-sectional shape is adjusted, perpendicularly to the z-direction, to the cross-section of the primary beam.
An X-ray optical system of this type is disclosed e.g. in the company document “HR-PHK for NanoSTAR” Instruction Handbook, Anton Paar GmbH, Kärntner Str. 322, A-8054 Graz (Austria), 1998, in particular, on page 16.
X-ray and neutron-optical methods are used to investigate the properties, i.e. material properties, of samples. Towards this end, a focussed X-ray or neutron beam is directed onto the sample where it interacts with the sample in a plurality of ways, in particular through scattering and/or diffraction. The X-ray or neutron radiation after the interaction process is registered by a detector and subsequently evaluated to obtain information about the properties of the sample.
In many of these methods, only a small part of the X-ray or neutron radiation is deflected in direction; the major portion of the radiation passes the sample without deflection. The non-deflected part of the radiation is called the primary beam, both in front of as well as behind the sample. Detectors for registering diffracted or scattered radiation must usually be protected from direct influence of the primary beam to prevent irreversible damage to the detector. Towards this end, so-called beam stops are used which partially shield the detector to prevent impingement of primary radiation. A beam stop can also shield disturbing divergent parasitic radiation (e.g. through Fresnel diffraction on collimator edges).
A conventional beam stop is described in the company document of Anton Paar GmbH loc. cit. The beam stop consists essentially of a gold plate which is fixed in a steel ring using nylon threads. The position of the gold plate in the annular plane (xy plane) can be adjusted with two micrometer screws. The steel ring is flanged to the detector.
The shape of the primary beam, in particular its diameter, depends on various factors. First of all, the components used such as diaphragms or the beam optics have production tolerances. Secondly, there are temporally varying properties of the beam optics, such as e.g. temperature influences, aging effects, or varying experimental structures.
To provide sufficient and reliable protection of the detector under these circumstances, a relatively large beam stop must be used which also shields part of the radiation in the region of small angle scattering (approximately 0.1 to 5° beam deflection), and information about the sample can be lost. Alternatively, the beam stop can be iteratively adjusted to a given beam optics. In this case, varying properties of the beam optics cannot be corrected.
In contrast thereto, it is the underlying purpose of the present invention to provide a method for operating a beam stop which protects the detector from the influence of the primary beam and divergent parasitic interfering radiation and at the same time permits passage of a maximum selectable part of diffracted or scattered radiation to the detector, wherein the beam stop can be easily adjusted to temporally varying properties of the beam optics.